sandbox/background-move/src/components/viewport.tsx

import react, { useCallback, useMemo, useState } from 'react';

import _ from 'lodash';

import Background from './background';

import '../theme/viewport.css';

const Viewport: react.FC<{}> = (props: {}) => {
  console.log(`--- Rendering viewport, props: ${JSON.stringify(props)} ---`);

  const [shift, setShift] = useState({ x: 1000, y: 1000 });

  const initialMouseState = {
    down: false,
    starting: { x: -1, y: -1 },
  };
  const [mouseState, setMouseState] = useState(initialMouseState);

  console.log('viewport, mouseState: ' + JSON.stringify(mouseState));

  const genericHandler = (event: any) => {
    console.log('Log - Event: ' + event.type);
    console.log(`Mouse : ${event.pageX}, ${event.pageY}`);
    console.log('mouseState: ' + JSON.stringify(mouseState));
  };

  // TODO: implement resize event
  // TODO: check boundaries

  const mouseDownHandler = (event: any) => {
    genericHandler(event);
    event.preventDefault();
    setMouseState({
      down: true,
      starting: { x: event.pageX, y: event.pageY },
    });
  };

  const mouseLeaveHandler = (event: any) => {
    genericHandler(event);
    event.preventDefault();
    throtteledMouseMoveHandler.cancel();
    setMouseState(initialMouseState);
  };



  const mouseUpHandler = (event: any) => {
    genericHandler(event);
    event.preventDefault();
    setMouseState(initialMouseState);
  };

  const mouseMoveHandler = (event: any) => {
    event.preventDefault();
    if (mouseState.down) {
      genericHandler(event);
      // setShift((shift) => ({
      //   x: shift.x + (mouseState.starting.x - event.pageX),
      //   y: shift.y + (mouseState.starting.y - event.pageY),
      // }));
      // setMouseState((mouseState) => ({
      //   down: true,
      //   starting: {
      //     x: event.pageX,
      //     y: event.pageY,
      //   },
      // }));
      setShift({
        x: shift.x + (mouseState.starting.x - event.pageX),
        y: shift.y + (mouseState.starting.y - event.pageY),
      });
      setMouseState({
        down: true,
        starting: {
          x: event.pageX,
          y: event.pageY,
        },
      });
    }
  };

  const throtteledMouseMoveHandler = useCallback(
    _.throttle(mouseMoveHandler, 50),
    [mouseState.down]
  );

  return (
    <div
      className='viewport'
      onMouseDown={mouseDownHandler}
      onMouseMove={throtteledMouseMoveHandler}
      onMouseUp={mouseUpHandler}
      onMouseLeave={mouseLeaveHandler}
    >
      <Background shift={shift} />
    </div>
  );
};

export default Viewport;